Water-soluble and -swelling resin coats designed to flow in water are made of such resins as polyvinyl alcohol, polyvinyl pyrrolidone and viscose with the aid of coating agents.
The aforesaid resin coats made of water-soluble resins by and large are satisfactory in terms of being capable of being allowed to flow in water.
However, in some applications where resin coats are required to retain their film forms stably in water for an initial certain short time without being swollen on their surfaces, there are diverse demands toward their minimum non-swelling time in water, depending upon what they are used for. Moreover, there are different requirements for how much soluble or swollen resin coats should be in water so as to be eventually allowed to flow in water, for instance, between industrial waste water disposal and life-related waste water disposal. A great deal of difficulty is thus involved in forming resin coats meeting such different requirements of a single resin.
For instance, water-soluble and-dispersible fibrous materials used as the supports of body fluid assay kits or devices are required to retain their resin coats stably in water for a certain, if not long, period of time. Yet it is very difficult to form a resin coat meeting such a requirement in a simple manner.
Until now, the supports for the aforesaid body fluid assay kits have been made of plastic sheets such as polystyrene sheets, because they should have a suitable degree of rigidity. However, such plastic sheet supports cannot be disposed of in toilet facilities after use, since they are neither soluble nor dispersible in water. Thus, it is a nuisance for the users to throw away them hygienically after use.
For that reason, body fluid assay devices comprising a test piece sheet of such water-soluble resins as polyvinyl alcohol and polyvinyl pyrrolidone (Japanese Patent Kokai Publication No. 62-24145) or a support obtained by making use of paper obtained by processing a fibrous component comprising pulp or regenerated pulp and a binder component comprising such a water-soluble resin as carboxymethylcellulose (Japanese Patent Laid-Open Publication No. 60-238763) by the paper-making technique have been proposed as toilet-disposable, water-dispersible body fluid assay devices.
In the first-mentioned body fluid assay device in which the support is made of a water-soluble resin, it is required that a plurality of films of the aforesaid water-soluble resin be laminated together in order for that support to retain the sufficient rigidity required for that body fluid assay device. This body fluid assay device is not only troublesome to assemble, but a time as long as 30 minutes or more is also needed for it to dissolve and disperse in water, when it has a thickness sufficient to achieve the aforesaid rigidity.
On the other hand, the second-mentioned body fluid assay device, whose support is made of paper obtained by the paper-making process using a fibrous component comprising pulp or regenerated pulp and a binder component of such a water-soluble resin as carboxymethylcellulose, is easy to handle because, once used, it can be disposed of in toilet facilities. A problem with this device, however, is that when the support is to be coated as by printing with an assay reagent layer, optionally with the reference color layer for determination, printing ink is likely to penetrate through the support. This makes it difficult to coat on the support the desired assay reagent layer optionally with the reference color layer for determination.
Some additional versions of body fluid assay devices have been proposed in Japanese Patent Laid-Open Publication Nos. 60-238763 and 1-121752, which include a support obtained by coating or laminating a water-soluble resin on either or both sides of paper prepared by the paper-making process using a fibrous component comprising pulp or regenerated pulp and a binder component of such a water-soluble resin as carboxymethylcellulose. These are said to retain shape during use and be disposable in toilet facilities.
However, the inventors' finding teaches that when a body fluid assay device making use of this support is immersed in a body fluid sample over too long a period of time, it cannot retain shape and tends to drop in terms of post-immersion rigidity. Thus, that body fluid assay device is less than satisfactory in terms of shape retention, since it sags at its end within the time of about 60 seconds required for coloration. Especially when a urine sample is injected directly onto the its reagent carrying region, its support is apt to suffer damage and so is less than satisfactory.